This invention relates to improvements in wood veneer clipper infeed conveyor systems and is herein illustratively described by reference to the presently preferred embodiment thereof. A broad object of the invention is to provide an improved veneer holddown device operatively associated with a veneer supporting infeed belt conveyor that overcomes certain prior art difficulties such as uncontrolled damage of jammed veneer and limited accessibility to remove crumbled veneer from the clipper entrance when a pileup occurs, and also such as unexpected breakage of elements that can enter the clipper unnoticed and cause damage to the blade and anvil parts.
In the course of a preliminary search regarding novelty of the invention, the following U.S. patents were noted as being of possible interest: U.S. Pat. Nos. 1,535,596; 2,038,770; 2,652,077; 3,244,044; 3,750,512; 3,837,250. These patents are believed to illustrate generally the state of the prior art on holddown and feed mechanisms of possible interest in relation to this invention. However, none suggests nor provides solutions to the problems of quickly clearing pileups of veneer in clipper machines, nor do they disclose an operable arrangement for minimizing damage to the veneer in the event of a pileup thereof at the entrance of a veneer clipper.
Typically, wood veneer emerging from a peeler lathe and advancing to the clipper does not lie flat, especially if peeled from an unsteamed log. Moreover, the veneer is not always in the form of a continuous uninterrupted sheet. The inevitable humps, waves and breaks in the veneer, and the occasional splinters and jagged edges that project out of the base plane of the veneer can cause the advancing sheet to catch on the clamp foot or other parts immediately adjacent to the clipper, thus causing a pileup. Inasmuch as the veneer is moving very rapidly (i.e., in the order of 300 or more feet per minute), an obstruction of this nature causes the oncoming veneer to crumble and roll up in a disordered pile very quickly. One requirement to minimize the jamming tendency is to clamp the veneer flat against the underlying conveyor surfaces up closely adjacent to and some distance ahead of the clipper, thereby presenting the veneer in flat planar condition to the maw of the clipper. However, unduly high clamping pressures must be avoided because of the greatly increased loading friction imposed thereby on the conveyor with a consequent unduly high feed power requirement. Moreover, even with precautions taken in the design of conventional veneer holddown mechanisms attempting to satisfy these requirements, obstructions still can and do occur. Accordingly, in addition to meeting these operating requirements, the present infeed conveyor holddown mechanism is further so constituted that, in the event of a pileup, it will retract its holddown elements in such a way as to provide immediate space relief to the veneer where it is most rapidly accumulating, followed by opening up additional space for convenient access to the veneer so as to permit its prompt removal without undue delays to restoration of normal functioning of the system.
A related object is to provide a motion-defining holddown mechanism that retracts the holddown bars in a sequential pattern permitting them to be reset under pressure against the veneer as closely as possible to the clipper and associated clamping shoe, thereby to minimize any tendency for curved veneer to catch and buckle the veneer advancing behind the clipper. In this same regard, the retraction motion is also so defined so as to minimize any tendency of the jammed veneer to interfere with the retraction.
Still another object hereof is to devise such a system wherein the mechanism is simple, rugged and reliable in operation, and the design of which overcomes former problems with mechanical breakage causing loose parts to damage the clipper elements.
A specific object hereof is to devise a retractable holddown mechanism with individually yieldable holddown bars that accommodate irregular passing humps and gaps in the veneer and when moving back downward thereafter, to do so with a forward component of forward motion, i.e., in the feed direction. As a result, the holddown bars maintain steady parallel tracking paths on the veneer without the necessity of providing heavy and expensive mounting structures on the bars to hold them in parallel relationship merely by mechanical support rigidty.
These and other features, objects and advantages of the invention will become fully evident from the following description by reference to the accompanying drawings.